JP2016104151A - Compact optic element for forming optic fiber beam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optic element (or a cap).SOLUTION: A cap 18 comprises at least one surface 25 which is formed as a lens, configured to direct light to outside of the cap 18 for focusing. The cap 18 is arranged by being attached to an optic fiber. Light radiation proceeds in a fiber, then interacts with one or plural optic surfaces of the cap 18, and as the result, beam which is focused or substantially collimated at certain distance on outside of the cap 18 is generated. The optic element such as the slender cap 18 can be used with various data collection modalities such as optic coherence tomography. A transparent film transmits light in a bi-directional state, and generates a controlled amount of back scattering. The film can surround a part of a beam directing tool.SELECTED DRAWING: Figure 1

Description

  The present invention generally relates to optical elements, design and manufacture of optical elements, and methods of using the same. In addition, the present invention also relates to the use of optical elements to collect data regarding the sample of interest.

  Optical analysis methods such as interferometry require delivering light to the sample of interest and collecting a portion of the light returning from the sample. Many light sources and light analyzers are typically located far from the sample of interest due to size and complexity. This becomes particularly apparent when the sample of interest is an internal part of a larger object, such as a biological tissue inside the living body. One way to optically analyze the interior part is to guide light from a distant light source to the sample using a thin optical fiber. A thin optical fiber is minimally disturbing the normal functioning of the sample due to the small cross section of the optical fiber. One example of such a method is the optical analysis of a luminal organ, such as a blood vessel, using a fiber optic catheter. Here, one end of the optical fiber catheter is connected to a light source outside the body, and the other end is inserted into a blood vessel.

  An important barrier to performing optical analysis of interior regions such as lumens is the design and low-cost production of miniature optical devices for focusing or collimating light. Many types of optical analysis, such as imaging and spectroscopy, require that light incident on the sample be focused or substantially collimated at a particular distance. Since light emanating from the tip of a standard optical fiber diverges rapidly, a small optical system can be coupled to the fiber to provide a focusing or collimating function. Furthermore, it is often desirable to analyze sample locations that are not directly on the optical axis of the fiber, such as analysis of the lumen wall of a thin blood vessel. In these situations, in addition to means for focusing or collimating light emanating from the tip of the optical fiber, means for substantially changing the direction of the light are used.

  A number of methods have been described so far for producing miniature optical systems suitable for attachment to optical fibers that provide some of the above functions. These methods generally include: 1) using graded-index (GRIN) fiber segments; 2) shaping the fiber tip directly into a lens; or 3) using a small bulk lens. One of the two methods is used to provide beam focusing means. Beam directing means are generally: 1) Use an angled reflective surface that uses total internal reflection (TIR) from the angled end of the fiber; 3) Small bulk mirror Or 4) provided using one of four methods: using a reflective coating on the fiber tip. However, these methods have a number of inherent limitations including excessive manufacturing costs, excessive size or focal spot size and insufficient freedom to select the focal length.

  Many miniature optical systems that can be used for analysis of internal lumen structure are known in the art. Each optical system is conceptually divided into beam focusing means and beam directing means. Light is passed from an external light source to an internal lumen through one or more light illumination fibers. The light illumination fiber may be single mode or multimode in nature. The illumination fiber is in communication with a miniature optical system that focuses and directs the beam into the lumen wall. Light is returned from the lumen to an analysis device outside the body using the same fiber or using another fiber co-located with the illumination fiber. In one type of miniature optics design, the focusing means and the orientation means are performed by separate optical elements. In another type of design, the focusing means and the orientation means are performed by the same element.

  Some features of existing optics are undesirable. For example, in some devices, all of the optical elements must be the same diameter as the optical fiber to minimize the overall system size (the diameter is often around 125 μm). This reduces the options available for selecting focus elements, beam expanders and beam directers, thus limiting the range of focal spot sizes and working distances achievable with the design. In addition, these extremely small elements are fragile, difficult to handle, and fragile during manufacturing and operation. Third, in many embodiments, it is necessary to provide an air gap in order to use the TIR to redirect the beam. This requires that a tight seal be maintained between the fiber and other elements to maintain the air gap. This can be a problem when the device is immersed in water, blood or stomach acid, or when the device is rotated or translated at high speed to form an image. Fourthly, the GRIN focusing element has a rotationally symmetric refractive index profile and cannot correct cylindrical aberration induced on the beam. The overall effect of these drawbacks is that certain miniature optics are expensive, difficult to manufacture, easily damaged, and do not produce a circular output at the focal plane.

  In addition to the drawbacks listed above, conventional lensed surfaces can only provide a small radius of curvature and are limited to generally spherical geometries. Furthermore, the beam cannot be expanded at any point in the optical system to a size significantly larger than the diameter of a single mode fiber (often 125 μm). These limits lead to a lens system with a limited working distance and considerable spherical aberration.

  As noted above, currently known miniature optical systems used to perform optical analysis or imaging have significant limitations. Thus, there is a need for optical elements that overcome the limitations of existing optical devices.

  In part, the present invention provides a unitary optical element (or cap) with an internal cavity that slides over the end of an optical fiber for internal or external analysis of the sample. The cap includes integrated surface features to change the beam direction and focus or collimate the light to a defined width at a defined distance away from the cap. The cap is small enough to prevent destruction or damage to sensitive samples such as internal body tissues or luminal organs. Since the cap is a single monolithic element in some embodiments, it can be made using low cost methods such as injection molding. Significant cost advantages and improvements in manufacturing repeatability are achieved compared to previously described methods.

  Certain embodiments of the present invention provide optical elements such as caps, covers or elongated members having a curved distal end face or surface. The optical element can be manufactured from a single piece of material that can be secured to and receive a section of optical fiber. In particular, the cap has an open end that receives the fiber, a length of solid material selected to be substantially optically transparent, and a curved reflective end surface that acts as both a lens and a mirror. Have In some embodiments, the curved reflective surface is shaped to have the focusing property of the lens and is coated to reflect (or partially reflect) incident light.

  Light is emitted from the optical fiber, travels through the solid material, and strikes the curved reflective end surface. The curvature of the lensed surface can be designed to focus or substantially collimate the incident light. The lensed surface can also be tilted with respect to the direction of propagation of light emitted from the fiber tip. The tilt angle is selected to reflect the light so that the light exits the cap through the side and reaches a focal point a desired distance away from the side.

  The above reflective attributes of the distal surface are obtained by coating the outer surface of the curved end surface with a reflective material such as a metal or dielectric material. Furthermore, the curvature of the lensed surface can vary along each of two orthogonal axes. Furthermore, the curvature of one axis can be independently adjusted to compensate for optical distortions imparted to the light as it exits through the substantially cylindrical side of the cap. The single piece configuration of the cap makes the cap amenable to manufacture by low cost methods such as injection molding.

  In certain embodiments, the present invention relates to a light beam directing element. The light beam directing element includes an elongated integral cap having a cylindrical outer surface with a longitudinal axis, the elongated integral cap being a distal end having a proximal end surface defining an annular opening and a beam directing surface. The elongated integral cap defines a solid section and a first cavity section defining a volume extending to a boundary of the solid section, the volume enclosing an optical fiber having a fiber end face The beam directing surface with respect to the fiber end surface, the light received from the fiber end surface being directed at a working distance D from the cylindrical outer surface and having a diameter w. At an angle and position to form a focal spot.

  In one embodiment, the elongated integral cap is formed from a material selected from the group consisting of acrylic resin, polycarbonate, polystyrene, polyetherimide, polymethylpentene, and glass. D can range from about 0 μm to about 30 mm. In certain embodiments, w ranges from about 3 μm to about 100 μm. The beam directing element may further include a stationary sheath and an optical fiber fixedly disposed within the volume, the optical fiber and the elongated integral cap configured to rotate within the stationary sheath. Is done. In some embodiments, at least a portion of the beam directing surface is coated with a reflective coating. The beam directing element may further include a lensed surface disposed within the cylindrical outer surface and formed from the boundary. In one embodiment, the beam directing surface is substantially flat. The reflective coating can include a partially transmissive coating.

  In one embodiment, the partially transmissive coating directs light from the fiber end face to form a focal spot having a diameter w directed at the working distance D from the cylindrical outer surface. The beam is split into a second beam that is directed at a working distance D ′ from the cylindrical outer surface to form a focal spot having a diameter w ′. Furthermore, the beam incident from the end face of the fiber can be divided based on the intensity of the incident beam or the wavelength of the incident beam. In one embodiment, a partially reflective coating is disposed on the distal section of the cylindrical outer surface. The arrangement is made such that a beam directed from the beam forming surface passes through the partially reflective coating and is reflected back from the partially reflective coating. A partially reflective coating can be disposed in the volume along a portion of the boundary. In some embodiments, the beam directing surface is located within the volume or the solid section. A second cavity section can be defined within the solid section such that the beam directing surface is partially shielded by a portion of the cylindrical outer surface surrounding the second cavity section. Further, the beam directing surface is shaped to substantially eliminate cylindrical light distortion induced by light propagating from the beam directing surface through the cylindrical outer surface and the stationary sheath. . In one embodiment, the beam directing surface is selected from the group consisting of a biconical aspheric surface, an aspheric surface, a biconical Zernike, Fresnel, and a non-uniform rational B-spline.

  In one aspect, the invention relates to a method for collecting optical data from a test sample in situ. The method includes providing an optical fiber including a core adapted to transmit a light beam having a first diameter; providing an elongated integral cap having a cylindrical outer surface and an annular opening. The cap is fixedly and optically coupled to the optical fiber by receiving and enclosing a length of the optical fiber in a cavity defined in the cap; Delivering to a mounting surface, the first light beam being directed from the cylindrical outer surface at a working distance D to form a focal spot having a diameter w. In certain embodiments, the method further includes splitting the light beam such that a second light beam is directed from the cylindrical outer surface to a working distance D ′ to form a focal spot having a diameter w ′. . In certain embodiments, the method further includes collecting optical coherence tomography data using the first light beam. In some embodiments, the method further includes generating one of the reference signals in response to a reflective element disposed within the integral cap, the reflective element being an interferometer in an optical coherence tomography system. Including the stage of working the arm. In certain embodiments, the method further comprises generating one of the calibration signals in response to a reflective element disposed within the integral cap, the calibration signal being a sample arm in an optical coherence tomography system. Used to adjust the reference arm optical path length to match the optical path length.

<Outline of Reference Reflector / Scattering Element Embodiment>
In one aspect, the invention relates to a fiber optic imaging probe having an elongated section and a proximal end and a distal end having a thin light scattering material applied to the distal end.

  In another aspect, the present invention relates to an optical element. The optical element includes a film or cover having a first surface and a second surface. The film includes a polymer and at least one backscattering element disposed therein for controlled optical backscattering. Furthermore, the membrane allows transmission of imaging light that is substantially undistorted.

  Aspects of the invention described herein can include further embodiments. For example, the optical element can further include a plurality of backscattering elements. Here, each of the at least one backscattering element and the plurality of backscattering elements is a particle having a certain particle size, and the plurality of backscattering elements are disposed in the polymer. In certain embodiments, the membrane is shaped to form a curved surface suitable for enveloping, enclosing, wrapping or otherwise covering an optical fiber end face or microlens.

  The particle size is less than about 1.5 μm in some preferred embodiments. In addition, the particles can include titanium, zinc, aluminum and / or other materials suitable for scattering light. The plurality of scattering elements can have a concentration of about 0.1% volume doping concentration. The optical element can further include an elongated member. Here, the membrane is shaped to form a sheath, in which the elongate member is disposed to form part of the probe tip.

  In one aspect, the present invention relates to an optical element. The optical element includes a bent cover having a first surface and a second surface. The cover forms part of an imaging probe, the cover including a polymer and at least one backscattering element disposed therein for controlled light backscattering, whereby the light A reference point is generated for the imaging system from the backscatter, and the cover allows transmission of the imaging light that is substantially undistorted.

  In another aspect, the invention relates to an imaging probe. The probe includes an elongate section having a first end and a second end, the second end forming a probe tip having an intraluminal imaging function, the probe tip comprising a scattering material. And the elongate section is adapted to transmit light reflected by the scattering material to the first end of the elongate section.

  In one embodiment, the elongated section is an optical fiber. The elongate section can also be a sheath. The probe may further include an optical fiber disposed in the sheath. The scattering material can include a plurality of light scattering particles dispersed in a substrate. The scattering particles can include titanium and / or other materials known to scatter light. The substrate can also include other polymers such as polyethylene terephthalate and / or urethane derivatives.

  In an embodiment of an aspect of the invention, the controlled amount of backscatter is an amount of light that is at least sufficient to generate a reference point in the imaging system for calibration of at least one imaging system parameter. It is. The substantially transparent film can also include a plurality of scattering particles.

  In yet another aspect, the invention relates to a method for calibrating an optical coherence tomography system. The method generates scan data in response to light reflected from the sample, and the reflected light passes through a bidirectional substantially transparent optical element; Generating reference data in response to scattered light reflected from a scattering element disposed within the element; calibrating the optical coherence tomography system to determine a relative longitudinal position of the scattering element; including.

  In one aspect, the present invention relates to a method for manufacturing an optical element. The method includes selecting a material suitable for intraluminal use in an animal; selecting a dopant adapted to scatter light in response to a light source, suitable for dispersion within the material. And determining a volume concentration of the dopant so that a radial scan of the doped material produces a defined backscatter.

  An embodiment of the present invention is an optical cap that can be secured to the end of a section of an optical fiber, an open end that receives the fiber, and an internal curved surface inline with the optical fiber that serves as a lens. A cap having a length of solid material and a closed end with a flat reflective end surface that acts as a mirror. In some embodiments, the reflective end surface is coated and in other embodiments it is not coated. The curvature of the internal lensed surface is chosen to focus or substantially collimate light emanating from the end of the optical fiber. The reflective end surface is made reflective by coating the outer surface of the end face with a metal or dielectric material. In one embodiment, the tilt angle between the end face and the fiber axis is generally about 45 degrees ± about 20 degrees.

  Another embodiment of the present invention is an optical cap that can be secured to the end of a section of an optical fiber, having an open end that receives the fiber, and an internal curved surface aligned with the optical fiber that serves as a lens. A cap is provided having a solid material of length and a closed end with a curved reflective end surface that acts as a second lens and mirror. The internal lensed surface is bent along one or two orthogonal axes to provide a first focusing means that acts on light emanating from the fiber tip. An end surface is also curved along one or more orthogonal axes and acts on light transmitted from the first lensed surface through the length of solid material. Provide focusing means. In certain embodiments, the end surface is made reflective by coating with a reflective material. In certain embodiments, the reflective material may be a metal or a dielectric material. In certain embodiments, the optical cap is an integral cap. Further, the optical cap can be made from one or more pieces of material in some embodiments.

  Yet another embodiment of the present invention is an optical cap that can be secured to the end of a section of an optical fiber, the open end receiving the fiber, a length of solid material, and a bent partial. A cap having a closed end with a reflective surface is provided. Light emanates from the tip of the fiber, travels through the solid material, and strikes a partially reflective surface. Some of the light is focused and reflected by the curvature of the surface and exits through the side of the cap. Another part of the light is refracted and transmitted through the end face of the cap. In this way, optical measurements can be performed simultaneously along two different axes. The end face is made partially reflective by coating its surface with a thin metal layer, a patterned metal layer, or with a thin dielectric film designed to partially transmit light. Is done.

  A further embodiment of the invention is an optical cap that can be secured to the end of a section of an optical fiber, comprising an open end that receives the fiber, a length of solid material, and a curved reflective surface. A cap is provided having a closed end with a side surface with a partially reflecting or backscattering coating. Light is emitted from the tip of the fiber, travels through the solid material, and strikes the reflective surface. The light is focused and reflected by the curvature of the surface and strikes the coated side of the cap. A portion of this light is transmitted by the coating and reaches a focal spot at a desired distance from the cap. Another part of the light is directly back-reflected or back-scattered by the coating and travels inside towards the original bent end face. The light is reflected again at the end face, refocused, and partially coupled to the end tip of the original optical fiber.

In this way, a controlled amount of reflected or backscattered light can be generated at some known distance from the focal spot. This is advantageous for use as a calibration signal or interference reference field in analytical techniques such as optical coherence tomography. The end face is made reflective by coating it with a metal or dielectric material. Sides can be partially coated with a material such as gold, aluminum or other metals, or coated with a thin dielectric film designed to partially transmit light, or small backscattered It is made partially reflective by coating with a layer of particles. Alternatively, the partially reflective attribute may be provided by a thin polymer tube impregnated with backscattering particles. The thin polymer tube is fixed over the outside of the optical cap. The thin polymer tube may be polyethylene terephthalate (PET) and the backscattering particles may be titanium dioxide. The reflective coating can also be selected from suitable dielectric reflective coatings. These dielectric reflective coatings can include multiple layers of dielectric material. For example, in some embodiments, alternating layers of TiO ₂ and SiO ₂ can be used to form a reflective coating.

  Yet another embodiment of the present invention is an optical cap that can be secured to the end of a section of an optical fiber having an open end that receives the fiber and a partially reflective coating aligned with the optical fiber. A cap is provided having an internal surface with a length of solid material, a closed end with a curved reflective surface, and a side with a partially reflective coating. Light is emitted from the tip of the fiber and strikes a partially reflective surface inside. Some of the light enters the original fiber as reflected or backscattered, while another part of the light is transmitted through the solid material and travels. In this way, a first amount of reflected or backscattered light can be generated at a known distance from the focal spot. The transmitted portion of light then strikes the reflective surface. The light is focused and reflected by the curvature of the surface and strikes the coated side of the cap.

  For this embodiment, a portion of this light is transmitted by the coating and reaches a focal spot at a desired distance from the cap. Another part of the light is directly back-reflected or back-scattered by the coating and travels inside towards the original bent end face. The light is reflected again at the end face, refocused, and partially coupled to the end tip of the original optical fiber. In this way, a second amount of reflected or backscattered light is generated at a known distance from the focal spot and at a known distance from the interior partially reflective surface. Can be done. This is advantageous for use as a calibration signal or interference reference field in analytical techniques such as optical coherence tomography. The end face is made reflective by coating it with a metal or dielectric material. The sides can be coated either partially with a metal material, or with a thin dielectric film designed to partially transmit light, or with a layer of small backscattering particles. Made partially reflective.

  In another embodiment, the present invention also provides a method of using various embodiments of the optical cap as a component in a fiber optic imaging catheter. The fiber optic imaging catheter is inserted into the luminal structure of a living body and connected to an optical coherence tomography system to obtain a high resolution image of the luminal structure.

  Yet another embodiment provides a means for protecting the lensed surface of the optical cap by positioning it partially or completely within the body of the cap. The cap may have any suitable geometric shape and is not limited to a cylindrical cap. Partial protection of the lenticular surface can be obtained by including an extension of the cylindrical body slightly proximal to the lenticular surface. In certain embodiments, partial protection of the lenticular surface can be obtained by completely positioning the lenticular surface within the cavity that receives the optical fiber. It will be appreciated that any of the above embodiments can be modified to include partial or complete protection of the lensed surface. These embodiments of the invention are not limited to protection-related features. For example, by denting the lensed surface, in some embodiments, it can be easier to guide the cap distally.

  The various embodiments described herein relate to subsystems for transmitting and receiving various types of electromagnetic radiation that can be directed through an optical fiber or similar waveguide. Thus, reference may be made to radiation, optical radiation, light or other types of electromagnetic radiation, but these terms are not intended to limit the scope of the invention, but instead lenses Or any type of light or electromagnetic radiation that can be sent or received by an optical fiber or similar waveguide.

The objects and features of the invention may be better understood with reference to the drawings and claims set forth below. The drawings are not necessarily to scale, with an emphasis on generally illustrating the principles of the invention. In the drawings, like numerals are used to indicate like parts throughout the various views. The drawings that accompany this disclosure are addressed individually within the present disclosure as they are introduced.
2 is a two-dimensional schematic cross-sectional view depicting an optical subsystem that directs a beam of light along an optical fiber through an elongated member defining a cavity, according to an exemplary embodiment of the invention. FIG. FIG. 3 is a three-dimensional view showing a reflective lensed end surface according to an exemplary embodiment of the present invention. 3 is a three-dimensional view of an optical element or cap, according to an exemplary embodiment of the present invention. FIG. 3 shows an optical cap that surrounds an optical fiber such that the cap is inside a transparent sheath, according to an embodiment of the present invention. Example ranges of focal spot sizes and working distances for lensed reflective surfaces of optical fiber tips and optical caps and three different lengths of solid material according to an exemplary embodiment of the present invention. FIG. In accordance with an exemplary embodiment of the present invention, a transparent lensed inner surface and an angle for directing the beam through the side of the cap and generating a focal spot at a desired distance from the cap. FIG. 3 shows an optical cap including a reflective end surface attached. In accordance with an exemplary embodiment of the present invention, a transparent lensed inner surface and an angle for directing the beam through the side of the cap and generating a focal spot at a desired distance from the cap. FIG. 3 shows an optical cap including a reflective end surface attached. In accordance with an exemplary embodiment of the present invention, includes a curved, partially reflective, lensed end surface for generating two focused beams directed through the side and end surfaces of the cap It is a figure which shows an optical cap. A curved, reflective, lensed end surface for directing the beam out of the side of the cap through a coating disposed on the outer cylindrical surface of the cap, according to an exemplary embodiment of the present invention. It is a figure which shows the optical cap containing. FIG. 4 illustrates an optical cap that includes a reflective or partially reflective surface in addition to a curved reflective lensed surface, in accordance with an exemplary embodiment of the present invention. FIG. 6 illustrates an optical cap in which a reflective lensed surface is protected from damage by being located within a volume defined within the cap, in accordance with an exemplary embodiment of the present invention. FIG. 7 illustrates an optical cap in which a reflective lensed surface is partially protected from damage by being partially positioned within the body of the cap, in accordance with an exemplary embodiment of the present invention. is there. FIG. 2 illustrates an apparatus for performing optical coherence tomography data collection, in accordance with an exemplary embodiment of the present invention. FIG. 3 illustrates a second apparatus for performing optical coherence tomography data collection, in accordance with an exemplary embodiment of the present invention. 1 is a diagram illustrating a mold for making an embodiment of the present invention. FIG. FIG. 14B illustrates an embodiment of the present invention fabricated using the mold depicted in FIG. 14A. 1 is a diagram illustrating a mold for making an embodiment of the present invention. FIG. FIG. 15C illustrates an embodiment of the present invention fabricated using the mold depicted in FIG. 15A. 1 is a schematic view of the tip of an optical fiber with a microlens and a protective cover. FIG. 6 depicts an image taken with a doped plastic lens cover.

  The following description refers to the accompanying drawings that illustrate certain embodiments of the invention. Other embodiments are possible and modifications may be made to these embodiments without departing from the spirit and scope of the present invention. The following detailed description is, therefore, not intended to limit the invention, but the scope of the invention is defined by the claims.

  The sections and headings of this application are not intended to limit the invention. Each section and heading is applicable to any aspect, embodiment or feature of the invention.

  It should be understood that the order of the steps of the method of the invention is not critical as long as the invention can function. Further, unless otherwise noted, two or more steps may be performed simultaneously or in a different order than that described herein.

  When a range or list of values is given, each value in the middle between the upper and lower limits of that range or list of values is considered individually, as if each value was clearly listed in this article. Included in the present invention. Further, smaller ranges are contemplated that lie between the upper and lower limits of a given range and include the upper and lower limits and are encompassed by the present invention. Citation of exemplary values or ranges does not exclude other values or ranges between the upper and lower limits of a given range and including the upper and lower limits.

  Unless otherwise noted, the terms “a” or “that” should be understood to represent “one or more”.

  These and other features and advantages of the present invention, as well as the present invention itself, will be more fully understood from the description, drawings, and claims.

  Advanced optical analysis or imaging developments such as confocal microscopy, single and multiphoton fluorescence imaging, harmonic imaging, optical spectroscopy and optical coherence tomography (OCT) It has had a tremendous impact on basic biological research and imaging under animal and human biological conditions. These methods differ in many respects, but have the common design feature that the incident light used to illuminate the sample of interest is focused or collimated. Focused light includes improved localization of incident light for better spatial resolution and increased optical power density to generate increased signal levels compared to unfocused light. Offer many advantages.

  A focused or collimated beam is generated by passing the output of the light source through a series of optical elements that together form an optical system. The elements of the optical system are selected to achieve a desired focal spot size that appears at a desired distance, referred to as the “working distance” from the last element of the optical system. The working distance is shown as an angle in the drawing. This is the preferred method of defining working distance (parallel to the direction of beam propagation). One preferred embodiment uses a beam that exits the side of the cap at a forward angle of ~ 10 degrees. Each individual optical analysis application has its optimal spot size and working distance. For example, confocal microscopy requires a small spot size close to 1 μm. On the other hand, OCT requires a medium spot size of about 5 to about 100 μm.

  While it is possible to obtain a wide range of spot sizes and working distances using an optical system consisting of conventional bulk lenses, many applications are for analyzing samples located inside larger objects Demanding a flexible and miniaturized optical system. Biomedicine is an example of a field where this demand is often found. Optical analysis of luminal structures such as esophagus, intestine, urinary tract, airways, lungs and blood vessels is sent through a flexible probe, focused using a small optical system, and extracorporeal data analysis through the flexible probe Light from an external light source returned to the system can be used.

  In addition, it is often desirable to analyze the luminal wall rather than the luminal content, such as using OCT to image the intima and media of the vascular wall rather than imaging blood contained in the blood vessel It is. This provides additional design objectives to direct the beam away from the longitudinal axis of the optical system or along another preferred direction (or range of directions). These types of optical probes are often “side-firing”, “side-directed”, “side-imaging” or “side-looking”. It is called. The size of these lumens may be as small as several millimeters, as in a blood vessel, which makes it very difficult to design a compact optical system. Furthermore, the embodiments described herein are suitable for use with various multi-fiber or fiber bundle embodiments. Various embodiments described below address these needs and others related to probe components and beamforming.

<Overview>
In general, the invention relates to an optical element having an elongated three-dimensional shape, such as a cap. The optical element defines a cavity or channel. The optical element can be sized to receive a portion of the optical fiber and to direct and focus the light in operation. The optical element can be fixed to an optical fiber and can be used to redirect and focus light outside the cap and to receive light from the sample of interest. The present invention provides a method for using a miniature optical cap and fiber as part of an insertable probe. The insertable probe can be used to perform optical analysis of the luminal structure in vivo. Other embodiments of the present invention deliver focused or substantially collimated light to a sample and return a portion of the light from the sample for processing in an imaging or data acquisition system. Also related to the design, manufacture and use of such devices. One exemplary non-limiting example of such a system is an optical coherence tomography (OCT) system.

<Beam forming element>
FIG. 1 shows an embodiment of the present invention suitable for forming a beam in place. In particular, an optical system 10 is shown that is suitable for directing light and collecting light or otherwise collecting data about the sample of interest. In the example shown, the optical fiber is connected at its proximal end to a light source (not shown). The optical fiber includes a light guiding core having a coated region 12 and a cladding region 14. In certain embodiments, the coated region 12 comprises a polyimide material. As shown in FIG. 1, the coating has been partially removed to expose a portion of the distal core and cladding in the coated region 12. As shown in FIG. 1, a protective material 16 such as an adhesive also surrounds the core and cladding 14 and / or the coated region 12. The optical fiber guides light radiation from the light source to a fiber segment distal to it. There, a certain length of the coating has been removed by a mechanical or chemical strip. The fiber end face (or fiber tip) can be flat or cut to a small angle, typically between about 8 ° and about 15 °, to prevent aberrations and unwanted back reflections. Can. This cutting action can be performed by a fiber cleaver. In certain embodiments, such cutting operations are quick and consistent, providing cost savings and manufacturing advantages.

  In general, in part, the present invention relates to an integrated optical element (or optical probe element or cap) 18 formed from a transmissive material. In one embodiment, the integrated optical element or cap has an elongated shape. In other embodiments, the optical element or cap is spherical or hemispherical. For example, in one embodiment, the cap is a sphere or a partially flattened sphere with fiber receiving holes formed in a non-diagonal direction, particularly 1/2 radius below the center of the sphere. However, any suitable cap geometry is possible. The optical element defines a bore or channel that extends through a portion of the optical element 18 until ending with a wall or region 19 formed from the transmissive material. As shown, the fiber core and cladding 14 and the coated region 12 are disposed within a volume defined within the cap 18 and enter the cap 18 through an annular opening 17 shown on the left side of the figure. . The present invention relates to various types and shapes of such optical elements that define channels, cavities or bores that partially surround or encapsulate an optical fiber, although the terms “cap”, “cover”, “optical assembly”, “Beam former”, “lens assembly” or other terms may be used in a non-limiting manner in this paper.

  Thus, in certain embodiments, the optical cap (or optical element) 18 includes a fiber-containing section 20 and a beamforming (or solid) section 21. Since a continuous monolithic material is typically used, a conceptual boundary indicated by a dotted line or boundary 22 distinguishes the first section 20 from the second section 21. The boundary 22 of the optical cap 18 can be imaged as defining a plane located distal to the adhesive or protective material 16 that fills the gap between the core 14 and the optical cap 18. As shown, in some embodiments, there is a gap between the fiber end face 23 (which may be inclined from about 8 ° to about 15 °) and the cavity wall 19. Further, as shown, an adhesive or protective material 16 fills the cavity including the core with the coated region 12 and the cladding 14. The optical element has a curved surface 25 distal to the fiber core with the cladding 14. The closed distal surface / curved end surface 25 can include one or more coatings, such as a reflective or partially reflective coating. Further, the optical element and fiber assembly are typically disposed within the sheath 28. In certain embodiments, the optical element 18 and other elements connected or fused thereto rotate together with respect to the sheath. In another embodiment, both the sheath 28 and the optical element 18 rotate. In another embodiment, the sheath and optical element 18 are fixed and do not rotate. Also, the region between the sheath and the optical element can be filled with fluid.

  In certain preferred embodiments, the optical element is a monolithic or unitary material. Although multiple combinations of materials such as polymers or glass mixtures can be used to make an optical element, generally the composition of the element is designed to be substantially the same throughout in certain embodiments. For a unitary optical element, a coating or other material may be applied, fused or otherwise coupled or connected.

  As shown in the embodiment of FIG. 1, the optical fiber core with the cladding 14 and the coated region 12 are inserted into the cavity on the proximal side of the optical element 18. Proximal and distal refer to the position relative to the end of the fiber that is connected to an extracorporeal instrument. The cavity (or fiber receiving chamber of the optical element) defined by the wall 19 can be filled with a protective material or adhesive 16 as shown. The adhesive 16 is selected to be substantially optically transparent and can be cured by exposure to ultraviolet light, heat, air, or any other curing method. In order to reduce the possibility of foam formation between the fiber end face 23 and the cavity wall 19, the application of the adhesive 16 may be carried out under a partial vacuum. To reduce back reflection, the material or adhesive 16 may be selected to have a refractive index that is close to that of the fiber 14 and optical element 18. Alternatively, the material or adhesive 16 may be selected to have a refractive index different from that of the fiber 14 and optical element 18 to produce a back reflection with a controlled amplitude. In some embodiments, the adhesive is an acrylic-based adhesive. In some embodiments, an adhesive that can be cured with ultraviolet light is used.

  In some embodiments, the cavity size is chosen to be very close to the fiber size to prevent tilt problems. The fiber end face is placed in contact with the end of the cavity to prevent longitudinal alignment problems. In some embodiments, this material 16 is an adhesive having a refractive index similar to that of the materials used to form the optical fiber core and element 18 so that back reflection from the fiber tip 23 is further reduced. is there.

  As the adhesive hardens (such as by exposure to heat, light or ultraviolet radiation), the fiber is secured to the cap in the volume or cavity shown. Alternatively, the cap can be formed at a location overlying the optical fiber core with the cladding 14 and the coated region 12 using a process such as injection molding. Forming the cap directly on the fiber eliminates the bonding step and can lead to reduced manufacturing costs. Thus, in some embodiments, region 16 has the same material filled region 18. That is, when the adhesive 16 is not used, the area defined in FIG. 1 is removed and the cap directly contacts the fiber.

  The cap has the general shape of a cylindrical tube with a closed distal surface. The outer diameter of the optical element 18 is typically on the order of twice the diameter of the optical fiber, giving an outer diameter range of about 160 μm to about 500 μm. The inner diameter of the optical element 18 can range from about 80 μm to about 250 μm.

  In certain embodiments, the cap 18 is made from a single piece of material selected to be optically transparent in the spectral band used for a particular imaging or analysis application. In general, the optical elements or caps described herein are suitable for use in imaging applications that use wavelengths of electromagnetic radiation that range from about 350 nm to about 2000 μm. To facilitate low cost and high volume manufacturing, the material can be a resin or polymer rather than glass. If low aberration levels and high transmission are desired for a given application, the cap can also be formed from glass. Preferred materials include acrylic, polycarbonate, polystyrene, polyetherimide or polymethylpentene. These materials can be injection molded into optical cap size / scale parts using methods known in the field of microfolding. In addition, these materials are suitable for forming an integral cap. In general, some embodiments of an elongated integral cap can include an optically transmissive material. As used in this article, optically transparent material means a material that has low absorption and scattering in the spectral band used for a particular application and that transmits a significant percentage of the light emitted from the optical fiber. To do.

  In certain embodiments, a single piece molded part provides a significant reduction in manufacturing cost and time and improvement in part and part uniformity compared to miniature optics known in the art as described above. provide. In certain embodiments, the length of the optical cap ranges from about 0.25 mm to about 5 mm. The air gap between the wall 19 and the end face 23 ranges from about 0 μm to about 1000 μm.

  Light traveling along the optical fiber exits the fiber end face 23 and the cavity wall 19 and propagates a length L into the solid material of the second section 21 of the optical element 18. The length L is equal to the distance from the cavity wall 19 to the center of the closed distal surface 25. As the light travels, the light diverges as indicated by the first set of dashed lines. Upon reaching the closed distal surface 25, the light interacts with the coating deposited on the outer surface of the distal surface.

  The coating is designed to be highly reflective in the spectral band used for specific imaging or analysis applications. The coating can be a metal, a single dielectric layer, or a multilayer dielectric stack. To improve adhesion, a layer without optical function may be deposited between the distal surface and the reflective coating. For example, such a layer can include chromium, titanium, or a dielectric. A layer without further optical functions may be deposited on the reflective coating. This is to protect the coating from oxidation, delamination or other damage.

  The normal to the center of the distal surface 25 is oriented at an inclination angle θ with respect to the longitudinal axis of the cap. Therefore, the reflected light is directed at an angle 2θ with respect to the incident light (see FIGS. 2A and 3). The distal surface 25 is further bent to form a focusing surface. Specific details of the focusing surface are described below. The light begins to focus or collimate after interacting with the distal surface 25 and the reflective coating. As light passes through the side 29 of the cap and the sheath 28, the light is affected by the cylindrical distortion due to the substantially cylindrical shape of the cap and sheath. This distortion causes the beam to be ovular in cross-section, resulting in a different focal plane for each of the two main axes of the beam. These two focal planes are separated in space along the direction of beam propagation.

  Cylindrical distortion is detrimental for many optical analysis applications because it leads to anisotropic lateral resolution, reduced peak incident power density and degraded axial resolution. However, the curvature of the distal surface 25 can be different in the two orthogonal axes in the plane of the distal surface, so that the lens is optimized to pre-compensate before cylindrical distortion occurs. Can be. In this way, a circularly symmetric beam is obtained outside the cap and the undesirable effects of cylindrical distortion can be avoided. Details of the distal face 25 geometry are fully described below.

  Once the light exits the cap, it continues to focus and eventually reaches a focal plane or spot that is a working distance D from the nearest edge of the optical element 18. If the fiber is a single mode fiber, the beam is Gaussian and its size in the focal plane is defined by a focal diameter w equal to twice the radius of the Gaussian profile of the beam. In certain embodiments, the length L and the geometry of the distal surface can be selected to provide a wide range of focal spot sizes and working distances. In some embodiments, D is an indicator as the distance from the side of the cap to the focal plane along the direction of beam propagation (not necessarily perpendicular to the cap). This approach is consistent with the way D is shown in FIG.

  If a long working distance is desired for a particular application, the length L can be increased. Thereby, the beam can be expanded to a longer diameter before hitting the distal surface 25. The beam can be expanded to a maximum diameter equal to the outer diameter of the cap, which can range from about 160 μm to about 500 μm. Increased beam expansion on the distal end is equivalent to increasing the aperture of the optical system. Increasing the aperture allows the working distance D to increase for a given focal diameter w. If a small focal diameter w is desired for a particular application, the radius of curvature of the distal surface can be reduced. This effectively increases the focusing power of the optical system.

<Geometric structure of the end face>
FIG. 2A is a three-dimensional perspective view of a lensized surface 40 (see surface 25 in FIG. 1) having a first focus F ₁ and a second focus F ₂ . FIG. 2B is a three-dimensional perspective view of the entire optical element or miniature optical cap 50 having an outer diameter A and an inner diameter D _i and an overall length B. As shown, the cap includes an annular opening 17 sized to receive and securely couple to the optical fiber. The focusing or beam forming surface 40 from FIG. 2A is implemented as surface 52 in FIG. 2B in one embodiment.

In general, in certain embodiments, the optical element is designed to form or direct a substantially circular symmetric beam that is substantially undistorted outside the optical element or cap. To facilitate this design feature, the distal surface is chosen to have a different curvature along the arc hit by rays Ax and Ay, corresponding to curves C ₁ and C ₂ on surface 40, respectively. Ax and Ay originate from different focal points F ₁ and F _2, respectively. For the optical element / cap described herein, a plurality of surface geometries 25, 40 including a biconical aspheric surface, a biconical Zernike, Fresnel or non-uniform rational B-splines are preferred. A biconical aspheric surface is typically used for applications requiring a focal spot size of about 3 μm to about 100 μm and a working distance of about 0 μm to about 30 mm, and the side of the cap and other materials located between the cap and the focal plane. This is suitable when it is desired to correct for the cylindrical distortion caused by.

  Returning to FIG. 2A, the deviation of the lensed surface away from a flat plane, such as the xy plane, commonly referred to as surface sag, is defined by .

プロットすると、この式は、レンズの曲がった表面の形をなぞる。個々のz値はxy平面に対する変動する表面たるみに対応する。

When plotted, this equation traces the shape of the curved surface of the lens. Individual z values correspond to varying surface sag relative to the xy plane.

In this equation, x, y, and z are local coordinates with an origin O at the center of the surface. R _x and R _y are spherical radii of curvature along the x and y axes, respectively. In the embodiment of FIG. 2A, Ax and Ay are examples of Rx and Ry. Furthermore, k _x and k _y are conic constants along the x and y axes, respectively, giving a total of four free parameters for surface sag z. The surface 40 is also rotated to an angle θ around the x axis to direct the surface beam at an angle 2θ. The surface can also be offset in the y direction by an amount y _off to further reduce aberrations of the optical system.

<Optimization of design parameters>
According to FIG. 3, an optical system 70 including a beam directing surface 72 for directing the beam out of the side of the cap 75 and generating a focal spot at a desired distance from the outer surface of the sheath 76 is shown. It is shown. Thus, in some embodiments, the beam directing surface directs and focuses a beam of light or other radiation. Further, the curvature of the lensed surface 72 can be adjusted to compensate for distortion caused by transmission through the sheath 76 and the outer cylindrical surface of the cap 75. The following sections are for designing a miniature optical cap of the type shown in FIG. 3 to achieve the desired focal spot size and working distance that are optimized for a particular optical analysis application. Describe the process. The optical analysis application chosen for this illustrative example is coronary vessel OCT imaging. This requires that the optical fiber and the miniature optical cap be rotated and translated in the longitudinal direction. This approach offers a number of advantages. Such benefits include:
Reduced manufacturing time saves costs and eliminates the need for fusion splicingProvides a non-rotationally symmetric lens shape that compensates for cylindrical distortionsPotentially improved reproducibility in focal spot size and working distance .

  FIG. 3 shows a miniature optical cap 75 encased in a flexible transparent sheath 76 having an inner diameter M and a wall thickness T. The fiber core with the cladding 14, the coated region 12 and the cap 75 are rotated and translated within the sheath by an external actuator. On the other hand, the sheath 76 remains stationary within the vessel to prevent damage to the vessel wall.

  In this illustrated example, the desired focal spot diameter w is about 30 μm. It is desirable for the beam to reach a focal plane at a distance D ′ from the side of the sheath 76 and a distance D from the cap. Here, D ′ is about 1.6 mm, and D is about 1.857 mm. The sheath wall thickness T is about 102 μm and the inner diameter M is about 710 μm. In order to allow sufficient clearance between the cap and the inner surface 77 of the sheath, the cap outer diameter A is chosen to be about 400 μm. In some embodiments, the cap material is chosen to be acrylic. This is because the material is optically clear at one wavelength of interest of about 1310 nm.

  In this example, the distal face tilt angle θ is selected to be about 50 ° to prevent unwanted back specular reflection from the inner surface 77 of the sheath 76. Thereby, incident light impinging on the distal surface is redirected at an angle of about 100 ° to the longitudinal axis of the fiber. The angle θ is shown as being formed between the longitudinal axis of the fiber and the normal vector to the surface 72. Thus, the light hits the inner surface of the sheath 77 at an angle of about 10 ° from normal incidence and back specular reflection is avoided. In certain embodiments, the lumen 78 between the cap and the sheath is filled with a radio opaque contrast fluid having a refractive index of about 1.449. Further, in certain embodiments, the lumen between the sheath 76 and the vessel wall is filled with the same contrast material or salt. The contrast material may be provided by a proximal flushing mechanism to temporarily drain blood from the blood vessel and allow for clear OCT images.

The design parameters that still need to be optimized are the distance L from the fiber tip to the lensed surface, the surface sag parameters R _x , R _y , k _x and k _y and y offset y _off (if any). . Optical simulation such as ZEMAX (ZEMAX Development, Bellevue, Washington, USA) to find the optimal combination of remaining design parameters to produce the desired focal spot diameter of about 20 μm at a distance of about 1.4 mm from the sheath -Tools or equivalent tools can be used. This software can also be used to ensure that the output beam hitting the vessel wall is circular and free of aberrations. To achieve this, a iterative optimization algorithm is used that searches for the best combination of free parameters that minimizes the value of the user-defined error function.

The error function measures several attributes of the simulated beam at the focal plane along the local x ′ and y ′ axes (see FIG. 3). The measured value is compared with the desired value and a weighted sum of the differences between the measured value and the desired value is generated to provide a value for the error function. The error function is the beam radius (Rx and Ry) at the 13.5% intensity level (corresponding to the characteristic radius ω ₀ of the beam) along the x ′ and y ′ axes, corresponding to the characteristic beam waist ω ₀ , x ′. Simulate Gaussian fit (Gx and Gy) along axis and y 'axis and distance (Fx and Fy) between desired focal plane and actual focal plane along x' and y 'axes Incorporated value is taken in. The error function is equal in beam diameter along the x 'and y' axes, Gaussian fitting is achieved, and between the desired focal plane and the actual focal plane along the x 'and y' axes. Constructed to give a value of 0 if the distance is equal to 0. If the beam diameters along the x ′ and y ′ axes are equal, the beam is circularly symmetric. This is desirable to produce an isotropic focal spot. If Gaussian fitting is achieved along the x 'and y' axes, the system has minimal distortion. This is desirable to maximize image quality and optimize the amount of optical power returned to the system for analysis. If these conditions are met, the beam is substantially free of aberrations and has the desired focal spot size w at the desired working distance D.

  In this illustrative example, the error function E may be chosen to incorporate six parameters including Rx, Ry, Gx, Gy, Fx and Fy. Each parameter is further assigned a weight W1 to W6 to control the relative importance of each parameter in the error function E. Each parameter is also assigned a target value Rxt, Ryt, Gxt, Gyt, Fxt and Fyt. Rx, Ry, Rxt, Ryt, Fx, Fy, Fxt and Fyt can be measured in millimeters. Gx, Gy, Gxt and Gyt are unitless parameters in the range of 0 to 1, with 1 representing a perfect Gaussian fit. The error function E is defined as the weighted sum of each parameter minus its corresponding target value. Therefore, E = W1 (Rx−Rxt) + W2 (Ry−Ryt) + W3 (Gx−Gxt) + W4 (Gy−Gyt) + W5 (Fx−Fxt) + W6 (Fy−Fyt).

In this illustrative example, Rxt and Ryt may be 0.017 mm, corresponding to a full width half maximum beam diameter of 0.020 mm. Gxt and Gyt may be 1. Fxt and Fyt may be zero. W1 and W2 may be 50, W3 and W4 may be 0.1, and W5 and W6 may be 1. Optical design values L, R _x, each selection of R _y, k _x, k _y and y _off is given a set of beam parameters Rx, Ry, Gx, Gy, the Fx and Fy, these parameters Now give a specific value for the error function E. Once parameter goals and weights are selected, one or more approaches to determine the combination of optical design values L, R _x , R _y , k _x , k _y and y _off that leads to the smallest error function Can be used for This can be achieved by finding a minimum in the error function or a minimum in the error function. Many optical design packages, such as ZEMAX, include built-in optimization algorithms that are sufficient to perform this step.

In this illustrative example, the optimization process results are about 721 μm L, about 772 μm R _x , about −675 μm R _y , about −3797 μm k _x , about −15,970 μm k _y and about − A y _off value of 23 μm is given. When these values are realized in the fiber optic cap embodiment, a focal spot size of about 29.6 μm can be formed at a distance D ′ of about 1600 μm. Such a focal spot size is suitable for performing OCT imaging and data collection in coronary vessels.

<Example focal spot size and working distance>
Embodiments of optical components such as caps or beamforming elements described herein include various distal surface surface geometries and various distances L (L ₁ , L ₂ between the fiber tip and distal surface. And a small optical cap with L ₃ ) allows a wide range of focal spot sizes and working distances. L ₁ , L ₂ and L ₃ are chosen for illustrative purposes and are not intended to limit the scope of the invention. In one embodiment, L ₂ was chosen as half of L ₁ and L ₃ was chosen as half of L ₂ . As an illustrative example, a plot of various data points using an acrylic cap having an outer diameter of about 400 μm is shown in FIG. In particular, FIG. 4 shows a subset of design parameters available for the acrylic cap discussed above. Here, the distance L from the fiber tip to the distal end face is selected to be one of about 2.10 mm, about 1.05 mm, or about 0.56 mm, respectively. These specific values of L are chosen merely for illustrative purposes and are not intended to limit the scope of the invention. In order to obtain a focal spot at a given working distance, the end face geometry at each point on each curve was optimized using the error function as described above according to the method described above.

  FIG. 4 shows that for this particular type of end cap, a focal spot size of about 4.3 μm to about 110 μm can be achieved at a working distance of about 0 mm to about 11 mm. For any given length L, the maximum working distance D ′ appears when the focal spot size approaches the size of the beam incident on the distal end face. Under this condition, the focusing power of the optical system is weak and the working distance cannot be extended any further.

<Internal lens surface>
FIG. 5 shows another optical subsystem 80 of the present invention. Here, the focusing of the beam is provided by the internal lensed surface 83 at the end of the cavity, not by the distal end face. The cap 85 has a different cavity shape due to the additional lensed surface 83. The surface 83 can be concave or convex, can have different radii of curvature in the x and y axes, can be spherical or non-spherical, or others commonly known in the art of lens design Can be any type of surface. Surface 83 allows for beam collimation or beam focusing and other features. In general, the shape of the surface 83 may be the same shape as shown in FIG. 2A. The surface 83 can be any type of lens surface. The surface 83 can be the same shape as shown in FIG. 2A. Here, the inclination angle θ can be as low as 0 degrees. This surface 83 acts like a boundary between the cavity and the beam forming section of the cap 85, similar to the boundary 19 of FIG. The beam direction is still provided by the distal end face 25 '. However, in this embodiment, the end surface is angled and is a flat surface.

  In certain embodiments, the end face 25 'is made reflective by coating it with a reflective material such as a metal or dielectric coating. In this embodiment, light emitted from the fiber tip spreads in the gap G. The gap may be filled with an optical adhesive to couple the fiber 14 to the cap 85, or alternatively, the gap may be filled with air to allow for faster beam expansion. The length of the gap G is set by the fiber length S and the cavity length S + G from which the protective coating has been removed.

  In one embodiment, a taper 87 on the proximal side of the cavity acts as a stopper for the coated portion of the fiber. Thereby, the insertion length of the fiber can be precisely controlled. Alternatively, a cylindrical stopper may be used instead of the taper. However, a tapered shape is generally preferred for microfabrication fabrication processes. In the micro-molding process, sharp edges are difficult to manufacture. The gap length G and the internal surface sag can be optimized in the same manner as described above using the error function. It is understood that if the cap 85 is placed inside the sheath (not shown), the gap length G and the surface deflection for the surface 83 can be further optimized to compensate for the distortion caused by permeation through the sheath. .

  This cap embodiment 85 provides several advantages in addition to those described above for the cap design shown in FIG. First, the lensed surface 83 is located within the cavity and protects it from accidental damage during handling or manipulation. Second, the area of the inner lensed surface 83 is less than the area of the distal end face 25 ', which simplifies the tool design used to make the cap. Thirdly, achieving a uniform coating layer thickness is simplified because the distal end face 25 'is flat rather than curved. The coating adhesion can also be improved due to the flatness of the end faces.

<Double lens surface>
FIG. 6 shows another optical subsystem 90 with a cap embodiment 95. Here, beam focusing is provided by a combination of one internal lensing surface 96 at the end of the cavity and a reflective lensing surface 97 formed at the distal end face. The beam direction is still provided by making the end face 97 reflective by coating with a reflective material such as a metal or dielectric coating. In this embodiment, the light emitted from the fiber tip 23 ′ spreads in the gap G. The light is refracted upon interaction with the inner lensed surface 96 and propagates through the solid material of length L ′. The light then strikes the distal end face 97 where it is further focused and redirected out of the side of the cap. The gap length G, the solid material length L ′, and the surface deflection of the inner surface 96 and the distal end surface 97 can be optimized in the same manner as described above using an error function. It will be appreciated that if the cap 95 is placed inside the sheath, the gap length G and the surface deflection of both surface 96 and surface 97 can be further optimized to compensate for the distortion caused by permeation through the sheath.

  This cap embodiment 95 provides several advantages in addition to those described above for the cap design shown in FIGS. First, by using two lensed surfaces 96, 97, more free design parameters are provided, allowing a wider range of focal spot size w and working distance D to be obtained. Second, the use of two lensed surfaces leads to less geometric aberration than a comparable design using a single lensed surface and improves the optical quality of the resulting beam. Third, the inner lensed surface 96 and the air gap G can be configured such that light transmitted through the length L ′ of the solid material is substantially collimated. In this way, the exact value of L ′ is less critical to the overall optical performance of the system, thereby improving the design tolerance for manufacturing errors. Under certain manufacturing conditions, the embodiment shown in FIG. 3, FIG. 8 or FIG. 11 is a preferred embodiment.

<Partially reflective end face for double beam scanning>
FIG. 7 illustrates another system embodiment 100 of the present invention that uses a cap 105. FIG. Here, the light emanating from the fiber tip 23 is split into two focused beams B ₁ and B ₂ by a partially reflective coating on the distal end face 107 of the miniature optical cap 105. In this embodiment, light emanating from the fiber tip 23 spreads into a solid material of length L. The light strikes the distal end face 107 where it interacts with the partially reflective coating. The coating transmits a portion of the light through the end face and reflects another portion of the light through the side of the cap. The reflected part B ₁ reaches the focal plane at the first working distance D with the focal spot size w. The transmitted part of the light B ₂ reaches the second focal plane at the second working distance D ″ with the second focal spot size w ″. It will be appreciated that if the cap is placed inside the sheath, the solid length L and distal end surface deflection can be further optimized to compensate for the strain caused by permeation through the sheath.

  The partially reflective coating referred to above can be formed in several ways. First, a highly reflective material, such as a metal, can be applied in a pattern on the distal end face so that the metal covers less than 100% of the end face area exposed by the beam. The pattern can include a checkerboard pattern, a ring shape, a concentric ring, or any other pattern. Second, a dielectric coating can be applied over a continuous portion of the end face area. The attributes of the dielectric material can be selected to partially reflect a fixed percentage of incident light power. Alternatively, the dielectric coating can be selected to substantially reflect one wavelength band and substantially transmit the second wavelength band. This type of coating is commonly referred to as a “dichroic” or “dichroic mirror” coating.

  The embodiment of FIG. 7 provides several advantages in addition to those described above for the cap design shown in FIGS. First, the generation of two beams B1, B2 along different axes allows simultaneous analysis of two different sample positions. This facilitates examining the luminal structure within the body. One illustrative example is OCT imaging of blood vessels containing occlusive lesions. With this embodiment, an annular image looking forward can be obtained simultaneously with a radial image looking sideways by rotating the catheter about the axis of the fiber. . In this way, an OCT image can be obtained from the front of the catheter when the catheter is advanced through the lesion to analyze the lesion structure.

  More generally, anterior imaging is useful for guiding the placement of the imaging catheter to avoid puncturing the lumen wall. When a dichroic coating is used, additional advantages are the optical analysis of the sample in front of the cap using a group of wavelengths and the optical of the sample on the side of the cap using a second group of wavelengths. It is possible to carry out statistical analysis. Thus, using such an approach, it is possible to perform multi-mode imaging of the luminal structure. OCT imaging can be performed using about 1310 nm light directed through the side of the cap, while confocal fluorescence imaging can be performed using about 800 nm light directed through the front of the cap.

<Fixed reflective surface>
In some optical analysis and data collection applications, including OCT imaging, it is desirable to include one or more surfaces that produce a reflection of known intensity at a known location relative to the focal plane. This facilitates calibration and interferometer calculations in some embodiments. The fixed reflection can be used in OCT applications to generate a calibration signal to adjust the reference arm length to match the sample arm length (see Petersen et al. US Patent Application Publication No. 2009/0122320, the disclosure of which is here). Incorporated by reference in its entirety). Fixed reflections can also be used in OCT applications to generate a reference field that interferes with the light returned from the sample. As a result, this forms a common path interferometer within the imaging catheter, avoiding the need for a separate reference arm.

  In part, the present invention allows the generation of a fixed reflection that includes only the calibration signal, only the reference field, or both the calibration signal and the reference field. FIG. 8 illustrates a system 110 embodiment of the present invention in which the coating 111 is applied to the side region of the miniature optical cap 113. Typically, a partially reflective or backscattering coating 111 is applied to a portion of the side of the optical cap to produce a controlled reflection at a known distance from the focal spot. As shown, the coating 111 overlaps the region of the side where the beam exits the cap 113. The coating 111 is chosen to be partially permeable. This can be accomplished using patterned metal coatings, thin film dielectric stacks or small backscattering particles. By using the coating 111, the fixed part of the light will be reflected from the coated part on the side. This reflected light strikes the bent distal surface 115 again and is coupled back into the optical fiber 14.

  The amount of reflected light that is desired to be coupled back into the fiber 14 depends on whether the fixed reflection is used to generate a calibration signal or a reference field. If an OCT calibration signal is desired, the intensity of light coupled back from fixed reflector 115 to fiber 14 should be comparable to the intensity of light returned from the sample to prevent saturation of the detection system.

  If an OCT reference field is desired, the intensity of light coupled back from fixed reflector 115 to fiber 14 should be several orders of magnitude higher than the intensity of light returned from the sample. This provides sufficient heterodyne gain for the sample light, thereby obtaining sufficient detection sensitivity for imaging in scattered tissue. However, since the coating 111 is not located at the focal plane of the optical system and rests on the cylindrically curved side of the cap, the back-reflected light is not perfectly coupled into the fiber. Thus, the reflectance or backscatter ratio of the coating is typically selected to be high enough to compensate for these fiber coupling losses. The loss can be calculated using optical design tools commonly used in the art.

  FIG. 9 shows another system embodiment 120 in which two fixed reflections are provided by two coatings. Specifically, in certain embodiments, a partially reflective or backscattering coating is applied to a portion of the side and the inner surface of the optical cap 121, and two controlled reflections at a known distance from the focal spot. Is generated. One coating 123 is located on a portion of the side of the cap and the other coating 124 is located on a portion of the interior surface of the cavity that receives the optical fiber 14. By generating two fixed reflections, the miniature optical cap 14 can provide one calibration signal and one reference field. Alternatively, two calibration signals can be provided, or two reference signals can be provided.

<Distal tip design for optical surface protection>
For some analytical applications, it is desirable to protect the optical surface of the small end cap from damage that may occur during catheter assembly or functional use of the device. FIG. 10 illustrates a system 130 that protects the optical surface 131 by placing it in an optical element or cap 133. Beam focusing is provided by an internal lensed surface at the end of the cavity that receives the fiber. The beam direction is provided by the same internal surface by tilting the surface with respect to the longitudinal axis of the fiber. The internal surface is made reflective by coating it with a reflective material such as a metal or dielectric coating.

  FIG. 11 illustrates a system 140 having an optical element 141 that provides partial protection of the optical surface 142. This may be sufficient to prevent damage in many applications. In this embodiment, the optical surface 142 is located in a recess formed by extending the cylindrical wall 144 of the cap distally beyond the end face. In this embodiment, the fiber 14 is in a first cavity formed in the optical element or cap 141 and the light directing surface 142 is in a second cavity formed at the distal end of the cap 141. It is formed.

<Imaging optical coherence tomography>
Various embodiments of the miniature optical cap described herein are suitable for performing OCT imaging of internal lumen structures. A flexible OCT imaging catheter can be constructed by wrapping the optical cap and fiber in a transparent sheath that covers the length of the catheter. The fiber and cap can then be rotated about the longitudinal axis of the fiber to perform a lateral spiral imaging. These various combinations of elements can operate as a data collection probe shown in the system embodiment of the appropriate drawing. If the cap is configured to generate a front looking beam in addition to the side looking beam as shown in FIG. 11, a forward-oriented annular image may also be obtained.

  FIG. 12 shows a data collection system 150 for performing OCT imaging using a flexible catheter that includes a small optical cap 155 at the distal tip. An optical cap 155 is secured to the flexible optical fiber 153 to form an insertable imaging catheter that directs light to the sample 157 and returns sample arm light to the OCT interferometer. The light source is in optical communication with the OCT interferometer, which can be a Michelson interferometer or any variation known in the art. The light source can be a broadband superluminescent diode, a tunable laser with a narrow instantaneous linewidth and a wide tuning range, a supercontinuum light source, or any source of low coherence light emission. The OCT interferometer is in optical communication with a reference arm that generates a reference field that interferes with sample light returned from the sample arm.

  The sample arm has an optical coupler and a flexible imaging catheter. The optical coupler connects to the proximal end of the catheter and directs some of the radiation from the light source into the catheter. The optical coupler also provides rotational and translational movement, which is transferred to the distal end of the catheter and a small optical cap. The light is guided through the fiber, focused by a small optical cap 155, redirected, and strikes the sample. As shown, the fiber and cap combination can rotate. Backscattered and back-reflected light from the sample is collected by a small optical cap, transmitted through the fiber, through the optical coupler, and transmitted back into the OCT interferometer. The sample arm light and the reference arm light interfere and are then detected, processed and displayed by the data acquisition and display system.

  FIG. 13 shows another system 170 for performing OCT imaging using a flexible catheter that includes a miniature optical cap 173 at the distal end. The optical cap has at least one fixed reflective surface as shown in FIG. 8 or FIG. The optical cap is secured to a flexible optical fiber 175 to form an insertable imaging catheter that directs light to the sample and returns sample arm light to the OCT interferometer. In addition, the optical cap 173 generates a fixed reference reflection at a known position relative to the focal plane. The reference reflection serves as an interference reference field and interferes with the sample light to form an optical coherence tomography image line. This configuration is known as a “common path” interferometer in the field of OCT imaging. Common-path interferometer embodiments have optical aberrations such as chromatic dispersion and polarization-induced dispersion in the sample and reference arms, which are common modes (the sample field and the reference field have substantially the same physical path). It is generated after passing), so it provides the advantage of matching. And matching these types of aberrations improves image resolution and contrast. However, certain types of common mode noise can no longer be canceled. Overall, the advantages of a common path interferometer are often more important than the shortcomings once a practical method for building a common path design is established.

  In this case, the fixed reflective surface is configured to generate a reference field that interferes with the sample light returned from the sample. Thus, the optical coupler and flexible catheter have an integrated reference arm and sample arm. This configuration has many advantages over the apparatus shown in FIG. First, since there is no separate reference arm, the cost and complexity of the system is reduced. Traditional OCT interferometers require a reference arm that is the same length as the sample arm. In this embodiment, the reference field is generated very close to the sample, so the reference arm path length is inherently matched to the sample arm path length.

<Embodiments of Manufacturing Process and Molding>
Any of the embodiments of the present invention can be manufactured from a single piece of material with application of the coating in one or more steps and subsequent steps. Alternatively, multiple pieces of material can be combined in a single step or multiple steps. In order to achieve low manufacturing costs and rapid manufacturing times, the manufacturing process may be any type of molding, including a special type of injection molding known as injection molding, compression molding or micromolding. FIG. 14A illustrates a mold 200 that includes four components that are used to produce an embodiment of the present invention using a molding process. A large two-part clamshell can be used to form the elongated cylindrical shape of the cap. A first core pin that gradually changes in diameter from approximately the outer diameter of the coated fiber region to the outer diameter of the core and cladding region can be used to form a cavity that receives the optical fiber. A second core pin with a diameter approximately equal to the diameter of the closed end face of the cap can be used to form an optical surface at the end of the cap. In essence, these core pins are placed in a mold and the material forming the final molded part flows around the pins and solidifies. FIG. 14B shows a molded part 205 that can be obtained using the mold tool 200 shown in FIG. 14A.

  An optical quality surface finish can be achieved by diamond turning the ends of the core pins. This process reduces aberrations resulting from surface roughness, thereby improving image quality. In addition, using the core pin, the optical surface is formed from a single molded piece, rather than machining half of the optical surface with each of the two clamshell mold pieces that form the cylindrical body of the cap. Can. Alternatively, the first core pin may be replaced by the optical fiber itself in the microforming process. This configuration, known in the art as “molding in place” or “over-molding”, positions the optical fiber within a half-cavity formed in the two clamshell components of the mold.

  FIG. 15A shows a mold 210 that includes three components that are used to make certain embodiments of the present invention using an overmolding process. In the overlay molding process, the optical fiber replaces the core pin that should have formed a cavity for receiving the optical fiber. During the molding process, the molten polymer flows directly onto the fiber and cures in-situ to directly form the molded part on the fiber. This process incorporates the fiber into the molded part, thus eliminating the need to adhere or separate and bond the fiber into the cavity of the molded part during subsequent assembly steps. FIG. 15B shows a molded part 215 that can be obtained using the mold tool shown in FIG. 15A. Here, the optical fiber is coupled to the elongated cap directly during the overlay molding process.

<Integrated Reference Reflector and Scattered Particle Embodiment>
FIG. 16 depicts an embodiment with an image wire tip of the probe. Optical fiber 270 terminates at microlens assembly 326. The microlens assembly 326 focuses light at a distance from the microlens assembly 326. Light emitted from the microlens assembly 326 is reflected by the beam deflector 330 and travels substantially perpendicular to the optical axis of the fiber 270. The entire fiber assembly is covered by a protective transparent sheath 334 doped with a small amount of scattering material to provide a reference reflection corresponding to the sample arm path length. This reflection is very useful in non-common path type interferometers (more typical types of interferometers). This is because the sample optical path and the reference optical path are physically different, but the path lengths must be matched to generate the required interference signal.

There are several materials as suitable dopants. In particular, titanium dioxide (TiO ₂ ) is advantageous. TiO ₂ is used in many paint formulations because of its excellent light scattering properties. Furthermore, it is inert and can be produced in large quantities. The particle size can be much smaller than the optical wavelength of interest (nominally 1.3 μm). This makes the scattering “Rayleigh” scattering. In this way, the wavefront of the outgoing and returning light is not significantly disturbed, thereby minimizing potential image degradation at sufficiently low dopant concentrations.

In addition, OCT imaging has tremendous sensitivity and large dynamic range (typically 100 dB sensitivity and> 60 dB dynamic range can be achieved with practical instruments), so optimal doping of TiO _{2 in} the material • Care must be taken to calculate the level and then achieve it.

  Basic scattering theory can be used to reach the doping concentration in the material. In a typical OCT image in the coronary artery, the instrument's minimum noise is about -100 dB. That is, about one billionth of the optical output power applied to the object of interest, and a typical image has a useful dynamic range of about 40 dB. The image processing electronics and software are optimized for this range, so the probe reflector element should be optimized to be near the maximum detectable peak of image intensity, which is about −60 dB (−100 + 40). This means that the probe reflector should be the brightest object in the image.

  As described herein, the probe reflector element can include, but is not limited to, a membrane, film, cap, cover, or other material. In some embodiments, the reflector element is flexible or inflexible. The reflector element can be shaped into various geometries. The portions of the reflector may be bent, planar, or substantially planar.

The basic scattering theory and classical radar cross section theory for particles is the ratio of the light reflected from a single TiO ₂ particle.
L _R = (σ _b / V _i ) l _c ΔΩ
Estimated to be given by Where L _R is the ratio of return light, σ _b is the scattering cross section (calculated from standard MIE theory), V _i is the volume of the particle, l _c is the interaction length (from radar theory), this In this case, the coherence length of the OCT light and ΔΩ is the light receiving angle (solid angle) of the microlens. Therefore, when the particle size is about 45 nm, the scattering cross section is about 4.26 × 10 ⁻⁷ μm ² , and the light with a coherence length of about 15 μm is irradiated through the microlens having a solid angle of ~ 0.004, the ratio of the reflected light L _R is about 0.006, that is, −32 dB.

Thus, the total light returned from the probe reference reflector element material should be equal to the volume fraction (doping concentration) multiplied by the proportion of single particle light. Since this should be equal to about -60 dB (from above), a reduction of -30 dB (or 0.001) is required. Thus, the volume fraction should be about 0.001 or about 0.1% doping volume concentration. This should lead to strong but not overwhelming reference reflections due to TiO ₂ particles, as shown in FIG.

  Thus, while certain embodiments of the invention have been described, various deviations, modifications and improvements will be apparent to those skilled in the art. Such variations, modifications, and improvements are intended to be within the spirit and scope of the invention. Accordingly, the foregoing description is by way of example only and is not intended as limiting.

Here are some notes.
[Appendix 1]
A light beam directing element having an elongated integral cap having a cylindrical outer surface with a longitudinal axis:
The elongate integral cap has a proximal end surface defining an annular opening and a distal end surface having a beam directing surface, the elongate integral cap comprising a solid section and a solid section of the solid section. Defining a first cavity section defining a volume extending to a boundary, the volume enclosing an optical fiber having a fiber end face and sized to receive the optical fiber, wherein the beam directing surface is relative to the fiber end face Are angled and positioned such that light received from the fiber end face is directed at a working distance D from the cylindrical outer surface to form a focal spot of diameter w.
Light beam directing element.
[Appendix 2]
The light beam directing element of claim 1, wherein the elongated integral cap is formed from a material selected from the group consisting of acrylic, polycarbonate, polystyrene, polyetherimide, polymethylpentene, and glass.
[Appendix 3]
The light beam directing element according to appendix 1, wherein D ranges from about 0 μm to about 30 mm.
[Appendix 4]
The light beam directing element according to appendix 1, wherein w is in the range of about 3 μm to about 100 μm.
[Appendix 5]
The light beam orientation of claim 1, further comprising a stationary sheath and an optical fiber fixedly disposed within the volume, wherein the optical fiber and the elongated integral cap are configured to rotate within the stationary sheath. Append element.
[Appendix 6]
The light beam directing element of claim 1, wherein at least a portion of the beam directing surface is coated with a reflective coating.
[Appendix 7]
The light beam directing element of claim 6 having a lensed surface disposed within the cylindrical outer surface and formed from the boundary.
[Appendix 8]
The light beam directing element of claim 7, wherein the beam directing surface is substantially flat.
[Appendix 9]
The light beam directing element of claim 6, wherein the reflective coating is a partially transmissive coating.
[Appendix 10]
The partially transmissive coating directs light from the fiber end face to the working distance D from the cylindrical outer surface to form the focal spot having a diameter w and the cylinder. The light beam directing element of claim 9, wherein the light beam directing element divides into a second beam that forms a focal spot having a diameter w 'directed at a working distance D' from the mold outer surface.
[Appendix 11]
The light beam directing element according to claim 10, wherein the beam incident from the fiber end face is divided based on the intensity of the incident beam or the wavelength of the incident beam.
[Appendix 12]
A partially reflective coating is disposed on a distal section of the cylindrical outer surface, the arrangement wherein a beam directed from the beam forming surface passes through the partially reflective coating; The light beam directing element of claim 1, wherein the light beam directing element is positioned to reflect back from the partially reflective coating.
[Appendix 13]
The light beam directing element of claim 1, wherein a partially reflective coating is disposed within the volume along a portion of the boundary.
[Appendix 14]
The light beam directing element of claim 1, wherein the beam directing surface is located within the volume or the solid section.
[Appendix 15]
The second cavity section is defined in the solid section, wherein the second cavity section is defined within the solid section such that the beam directing surface is partially shielded by a portion of the cylindrical outer surface surrounding the second cavity section. Light beam directing element.
[Appendix 16]
The beam directing surface is shaped to substantially remove cylindrical light distortion induced by light propagating from the beam directing surface through the cylindrical outer surface and the stationary sheath. 5. The light beam directing element according to 5.
[Appendix 17]
6. The light beam directing element of claim 5, wherein the beam directing surface is selected from the group consisting of a biconic aspheric surface, an aspherical surface, a biconical Zernike, Fresnel, and a non-uniform rational B-spline.
[Appendix 18]
A method of collecting optical data from a test sample in a natural position:
Providing an optical fiber including a core adapted to transmit a light beam having a first diameter;
Providing an elongate integral cap having a cylindrical outer surface and an annular opening, wherein the cap receives and surrounds a length of the optical fiber within a cavity defined within the cap. Fixed and optically coupled to the stage;
Delivering the light beam to a beam directing surface such that the first light beam is directed from the cylindrical outer surface at a working distance D to form a focal spot having a diameter w.
Method.
[Appendix 19]
The method of claim 18, further comprising splitting the light beam so that a second light beam is directed from the cylindrical outer surface to a working distance D 'to form a focal spot having a diameter w'.
[Appendix 20]
The method of claim 18, further comprising collecting optical coherence tomography data using the first light beam.
[Appendix 21]
Appendix 18 further comprising generating one of the reference signals in response to a reflective element disposed within the integral cap, the reflective element serving as an interferometer arm in an optical coherence tomography system. the method of.
[Appendix 22]
Generating a calibration signal in response to a reflective element disposed within the integral cap, wherein the calibration signal matches a sample arm path length in an optical coherence tomography system. The method of claim 18 used to adjust

Claims (7)

An apparatus for imaging a blood vessel using an optical coherent tomography probe comprising an optical fiber disposed within an elongated cap,
Means for transmitting light from a light source along the optical fiber, the optical fiber having the end face such that diverging light propagates from the end face;
Means for transmitting the diverging light through a beam directing surface of the elongate cap such that strain compensated light propagates from the beam directing surface;
Through the strain-compensated light through the outer surface of the elongate cap and a flexible sheath surrounding the elongate cap, cylindrical light distortion from the outer surface and the flexible sheath is substantially eliminated. And means for communicating,
Means for imaging a blood vessel in response to light received from the flexible sheath using light scattered from the blood vessel;
Including the device.   The apparatus of claim 1, wherein the means for imaging the blood vessel further comprises generating an image of the blood vessel using optical coherence tomography.   The apparatus of claim 1, further comprising means for reflecting light from the beam directing surface in response to a coating disposed on the beam directing surface.   The apparatus of claim 1, further comprising means for transmitting the diverging light from the end face of the optical fiber.   The apparatus of claim 1, wherein D ranges from about 0 μm to about 30 mm.   The apparatus of claim 1, wherein w ranges from about 3 μm to about 100 μm. A method of imaging a blood vessel using an optical coherent tomography probe including an optical fiber disposed within an elongated cap, the method comprising:
Transmitting light from a light source along the optical fiber, the optical fiber having the end face such that diverging light propagates from the end face;
Transmitting the diverging light through the beam directing surface of the elongate cap such that strain compensated light propagates from the beam directing surface;
Through the strain-compensated light through the outer surface of the elongate cap and a flexible sheath surrounding the elongate cap, cylindrical light distortion from the outer surface and the flexible sheath is substantially eliminated. And the stage of communicating,
Imaging a blood vessel in response to light received from the flexible sheath using light scattered from the blood vessel;
Including methods.

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